1. Field of the Invention
The present invention relates to a fuel injection nozzle for an internal combustion engine and a manufacturing method thereof.
2. Description of Related Art
A direct fuel injection system is known in the art. In the direct fuel injection system, fuel is directly injected into each corresponding combustion chamber of an internal combustion engine to reduce fuel consumption and emissions and to increase engine power. In the direct fuel injection system, appropriate atomization of fuel is an important factor to be considered to improve combustion characteristics in the combustion chamber. In an injector of the fuel injection system, initiation of fuel injection and stop of fuel injection need to be effectively performed through opening and closing of an injection hole of the injector. However, fuel generally includes impurities, such as high boiling components, additives or water. Due to influence of, for example, the ambient temperature, the impurities can be adhered to and accumulated in the injection hole or a region around the injection hole as debris. When the debris is adhered to and accumulated in the injection hole or the region around the injection hole, flow of fuel is disturbed, and thus injection of fuel through the injector can not be precisely controlled.
To address this disadvantage, for example, Japanese Unexamined Patent Publication No. 9-112392 discloses a technique for forming a coating, which is made of a lipophobic material, in an outer wall of a fuel injection nozzle and an inner wall of the injection hole. With this coating, it is possible to restrain accumulation of debris in the fuel injection nozzle, particularly in the fuel injection hole and the region around the fuel injection hole, so that a reduction in the amount of fuel injected from the injection hole or a change in a spray pattern of fuel injected from the injection hole is advantageously restrained.
However, debris can be formed from residual fuel in an interior of the nozzle, i.e., in a space defined between a nozzle needle and a nozzle body. That is, the debris can be adhered not only to the outer wall of the nozzle body and the inner wall of the injection hole but also to the nozzle needle. Thus, in the case of the Japanese Unexamined Patent Publication No. 9-112392 where the coating layer is formed in the outer wall of the fuel injection nozzle and the inner wall of the injection hole, it is not possible to restrain accumulation of the debris around an engaging portion of the nozzle needle. Particularly, in the case of a direct injection engine, hot combustion gas is introduced into the interior of the nozzle through the injection hole at the time of combustion. Thus, for example, residual fuel, which remains in the space between the nozzle needle and the nozzle body, can be carbonized by the heat and can be accumulated as debris in the distal end of the nozzle needle.
When the debris is accumulated in the nozzle needle, flow of fuel in the injection nozzle is agitated, or flow of fuel is disturbed. As a result, the amount of fuel injected from the injection hole could be disadvantageously reduced, or the spray pattern of fuel injected from the injection hole can be disadvantageously changed. Furthermore, when debris is accumulated around the engaging portion between the nozzle needle and the nozzle body, fluid tightness at the engaging portion could be possibly deteriorated.